Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: O que mostra para 2006 quando 1999 é Grand Slam Tournaments?
 ###Tabelas: CREATE TABLE inter-cities_fairs_cup_uefa_cup_uefa_europa_league (inter-cities_fairs_cup_uefa_cup_uefa_europa_league_id AUTO_INCREMENT PRIMARY KEY, Year VARCHAR, Team VARCHAR, Progress VARCHAR, Score VARCHAR, Opponents VARCHAR) CREATE TABLE commentators_and_spokespersons (commentators_and_spokespersons_id AUTO_INCREMENT PRIMARY KEY, Year(s) INT, Grand Final Television Commentator VARCHAR, Grand Final Dual Television Commentator VARCHAR, Spokesperson VARCHAR, Semi Final Television Commentator VARCHAR, Semi Final Dual Television Commentator VARCHAR) CREATE TABLE singles_performance_timeline (singles_performance_timeline_id AUTO_INCREMENT PRIMARY KEY, Tournament VARCHAR, 1990 VARCHAR, 1991 VARCHAR, 1992 VARCHAR, 1993 VARCHAR, 1994 VARCHAR, 1995 VARCHAR, 1996 VARCHAR, 1997 VARCHAR, 1998 VARCHAR, 1999 VARCHAR, 2000 VARCHAR, 2001 VARCHAR, 2002 VARCHAR, 2003 VARCHAR, 2004 VARCHAR, 2005 VARCHAR, 2006 VARCHAR, 2007 VARCHAR, 2008 VARCHAR) CREATE TABLE standings (standings_id AUTO_INCREMENT PRIMARY KEY, Locale VARCHAR, Skip VARCHAR, W INT, L INT, PF INT, PA INT, Ends Won INT, Ends Lost INT, Blank Ends INT, Stolen Ends INT, Shot Pct. INT) CREATE TABLE doubles (doubles_id AUTO_INCREMENT PRIMARY KEY, Tournament VARCHAR, 1998 VARCHAR, 1999 VARCHAR, 2000 VARCHAR, 2001 VARCHAR, 2002 VARCHAR, 2003 VARCHAR, 2004 VARCHAR, 2005 VARCHAR, 2006 VARCHAR, 2007 VARCHAR, 2008 VARCHAR, 2009 VARCHAR, 2010 VARCHAR, 2011 VARCHAR, Career W/L VARCHAR)  
SELECT 2006 FROM singles_performance_timeline WHERE 1990 = grand slam tournaments